Get a bike that you can mount a babyseat/babytrailer to. Ride what you have and in a year or so if you find yourself riding all your bikes, return to your one bike a year plan. Kids change your life and they will provide more comfort in your old age than any silly bike will. Look forward to the day when you can go riding with your kids. And make sure you don't end up with a third one unless it's your choice.

Of course, this thread has already started morphing into a totally different subject.